In modern packaging machines for the manufacture of, for example, parallelepipedic packages or cartons for liquid contents such as juice or milk, a web-shaped flexible packaging material is progressively formed into a tubular so form that both longitudinal edges are united and sealed together. After the supply of the desired contents to the packaging material tube, the tube is transversely sealed at even spacing and is severed for the formation of individual packages or cartons which, by possible additional forming processing, may be given the parallelepipedic configuration. The reforming of the originally planar packaging material into tubular form takes place with the aid of forming devices which, inter alia include forming rollers which are annularly disposed about a substantially circular aperture for the packaging material. The forming rollers are freely rotary and together force the packaging material to assume a substantially circular cross-section so that its longitudinal edges may be sealed to one another.
The annularly disposed forming rollers have hitherto normally had conical end surfaces which are located slightly spaced from one another or substantially abut against one another along a line directed from the center of the rollers towards the center of the packaging material tube. In particular in the employment of thin and highly flexible packaging material--as is the case in the manufacture of small carton sizes--it may happen, in such a situation, that the packaging material is entrapped in the nip between the end walls of two mutually adjacent forming rollers so that a longitudinal crease line is formed on the packaging material tube, which occasionally results in rupture of the entire material web or, in any event, gives the subsequent tube on incorrect configuration. With a view to obviating this drawback, attempts have been made in the art to adjust the mutual spacing of the forming rollers so that minimum clearance, or even no clearance occurs between the ends of the forming rollers, but such attempts have enjoyed only limited success and this problem still defies solution in the case of extremely thin packaging material types.
There is, hence, a need in the art to devise, in that type of packaging machine which manufactures packages or cartons from web-shaped flexible material, an apparatus for forming the tube which does not suffer from the above-considered drawbacks.